Per Jellycat rules and regulations from their website:

We are unable to offer our paper books or board books in the state of California because they do not meet the state’s strict limits for acrylamide under Proposition 65.

Although the health risks associated with acrylamide are mainly linked to cooking certain foods, California’s regulations are broad enough to include potential trace amounts found in paper products.

These same books meet all standards in other U.S. states and international markets where they remain available.